Field of the Invention
The invention relates to a multilayer sheet having high compressive strength, high heat resistance and low permeability relative to fluids, including layers of graphite foils and metal foils alternatingly disposed one upon another and parallel, with the graphite foils joined to the metal foils.
Such multilayer sheets are used, in particular, in sealing technology and for impermeable linings. U.S. Pat. No. 5,128,209 describes a gasket material being formed of layers of a fluoropolymer, graphite foils and metal foils, with the layers being bonded together by an adhesive. The layers of the fluoropolymer are made of material which is porous and therefore permeable to fluids. They impart a greater stability, toughness, tensile strength and an improved handling to that component of the composite being formed of the graphite foils and the fluoropolymer foils. The disadvantages of that gasket material are firstly the permeability of the fluoropolymer foils to fluids and the presence of adhesives as bonding agents between the layers. The fluoropolymer foils contribute virtually nothing to the impermeability of the overall system, which has an adverse effect especially in the case of gaskets for high and extreme impermeability requirements. The adhesives are a weak point, especially in the case of gaskets subjected to high pressures or stresses, because the layers of the multilayer sheet can slide on them. That ultimately leads to the non-operability of the gasket or, in particular in co-operation with elevated temperatures, to fine cracks occurring in the adhesive layer which impair the sealing effect.